Lubricating oil additives

ABSTRACT

The addition of minor amounts of an asphaltene and a zinc 0,0di-alkylphosphorodithioate minimizes viscosity increases of mineral lubricating oils containing hydrogenated butadienestyrene copolymer VI improvers when subjected to extreme operating conditions that ordinarily cause substantial viscosity increases. The compositions are not subject to substantial viscosity increases when heated to elevated temperatures for prolonged periods.

[ Feb. 19, 1974 LUBRICATING OIL ADDITIVES [75] Inventor: William G.Billings, Bartlesville,

Okla.

[73] Assignee: Phillips Petroleum Company,

Washington, DC.

[22] Filed: July 13, 1970 [21] Appl. No.: 54,651

[521 US. Cl. 252/32.7 E, 252/47.5, 252/59 [51] Int. Cl. Cl0m 1/48, ClOmH38 [58] Field of Search 252/32.7 E, 47.5, 75, 59; 44/68 [56] ReferencesCited UNITED STATES PATENTS 1,708,563 4/1929 Black et a1 252/592,778,780 1/1957 Romberg 252/59 3,041,282 6/1962 Gordon et al 252/593,250,709 5/1966 Morway et al. 252/39 3,523,082 8/1970 Vienna et al252/32.7 E 3,554,911 l/197l Schiff et a1 252/59 3,630,918 12/1971 Hottenet a1. 252/32.7 E

3,376,221 4/1968 Butler 252/32.7 3,442,804 5/1969 Le Suer et a1.252/32.7

Primary ExaminerDaniel E. Wyman Assistant Examiner-l. Vaughn Attorney,Agent, or Firm-Young and Quigg [5 7 ABSTRACT The addition of minoramounts of an asphaltene and a zinc 0,0-di-alkylphosphorodithioateminimizes viscosity increases of mineral lubricating oils containinghydrogenated butadiene-styrene copolymer V1 improvers when subjected toextreme operating conditions that ordinarily cause substantial viscosityincreases. The compositions are not subject to substantial viscosityincreases when heated to elevated temperatures for prolonged periods.

4 Claims, No Drawings BACKGROUND OF THE INVENTION This invention relatesto improved lubricating oils and processes of preparing the same. Inaccordance with another aspect, this invention relates to the additionof asphaltenes and a zinc 0,0-dialkylphosphorodithioate to lubricatingoils containing polymeric VI improvers to improve the viscositycharacteristics of the lubricating oil formulation when subjected tohigh temperatures for prolonged periods of time. In accordance with afurther aspect, this invention relates to lubricating oil formulationscontaining hydrogenated butadiene-styrene copolymers as VI improvers towhich has been added the combination of an asphaltene and a zinc0,0-dialkylphosphorodithioate to minimize the viscosity increase of theoil formulation when subjected to extreme operating conditions thatordinarily cause sub stantial viscosity increases.

As is well known, the viscosity of lubricating oils varies with thetemperatureMany oils must be employed over a wide temperature range,e.g., F to 300F, and it is important that the oil not be too viscous atlow temperatures or too thin at high temperatures. Variation of theviscosity temperature relationship of an oil is indicated by thewell-known viscosity index value. The higher the viscosity index, theless the change in viscosity with change in temperature. Viscosity at210F and at 100F is used to determine the viscosity index.

Many attempts have been made to improve the properties, particularly theviscosity-temperature relationship and shear stability, of lubricatingoils. It has been proposed to add various materials to the lubricatingoils for this purpose. Although some of the prior art additives have metwith some success, most do not minimize the viscosity increase oflubricating oils when heated to elevated temperatures such as 300F forextremely long periods of time.

In accordance with the invention, I have discovered that the addition ofminor amounts of an asphaltene and a zinc 0,0-dialkylphosphorodithioateminimizes the viscosity increase of lubricating oils when heated to andmaintained at an elevated temperature for prolonged periods of time.

Accordingly, an object of this invention is to improve lubricating oilsand especially the viscositytemperature relationship of minerallubricating oils.

Another object of this invention is to improve lubricating oils byadding specific additives thereto to stabilize the viscositycharacteristics of the oil when subjected to high temperature operatingconditions.

A further object of this invention is to provide new and improvedmineral lubricating oils and methods of preparing the same.

Other aspects, objects and the several advantages of the inventionwillbe apparent to those skilled in the art upon further study of thespecification and appended claims.

I SUMMARY OF TI'IE INVENTION In accordance with the invention,lubricating oils exhibiting minor viscosity increases when heated to ahigh temperature and maintained at an elevated temperature for prolongedperiods are produced by addition of minor amounts of a combination of anasphaltene and a zinc 0,0-dialkylphosphorodithioate to the oil.

In accordance with one embodiment of the invention, a lubricating oilcontaining a hydrogenated butadiene-styrene copolymer as a VI improveris improved with respect to its viscosity characteristics when subjectedto high temperature operating conditions by the addition of anasphaltene and a zinc 0,0- dialkylphosphorodithioate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The zinc0,0-dialkylphosphorodithioates that can be employed according to thisinvention are represented by the formula:

i -S-ZnS-i R-oon wherein R is an alkyl having from 2 to 30 carbon atoms,the Rs can be the same or different, and they can have the same ordifferent number of carbon atoms.

Examples of specific compounds which can be used include: zinc0,0-diethylphosphorodithioate, zinc 0,0- diisopropylphosphorodithioate,zinc 0,0-di-npropylphosphorodithioate, zinc0,0-dibutylphosphorodithioate, zinc0,0-di-4-methyl-2-pentylphosphorodithioate, zinc0,0-di-3,3-dimethyl-2-butylphosphorodithioate, zinc0,0-didecylphosphorodithioate, zinc 0,0-dieicosylphosphorodithioate,zinc 0,0- triacontylphosphorodithioate, zinc0,0-diamylphosphorodithioate, and mixtures thereof.

The zinc 0,0-dialkylphosphorodithioate compounds that can be employedaccording to the invention are well known in the art and can be preparedaccording to any known procedure. For example, mixtures of alkyls inthese compounds can be prepared as described in US. Pat. No. 3,442,804.

The amount of zinc 0,0-dialkylphosphorodithioate employed can range from0.5 to 1.2 weight per cent, preferably from 0.90 to 1.05 weight percent.

The asphaltenes that can be employed according to the invention arederived from conventional sources by conventional techniques. Knownasphaltic products containing asphaltenes that can be used as additivesaccording to the invention include heavy asphaltic crude oils, straightrun residues of asphaltic crude oils, solvent tars produced by treatmentof residues, cracked,

residues, and various petroleum asphalts. The asphaltenes can beseparated, for instance, from crude oils or other asphaltic sources byextraction with pentane or similar hydrocarbon solvents or other knownsolvents to separate same from the crude.

' The asphaltenes can be characterized as particulate materials and havethe following characteristics as set forth in the PETROLEUM REFINER,Vol. 31, No. 2, page 138, February 1952: a

Asphaltenes seem to be constant in composition, despite source, asdetermined by carbon-hydrogen analysis. They vary, however, in molecularweight. Determination of asphaltenes is standardized, and the fractionis variously termed as pentane, hexane, or naphtha insoluble, dependingupon the precipitant used. In character, asphaltenes are predominantlyaromatic. Ultimate analysis of Thurston and Knowles (IEC 28, No. 1, pp.88-91, 1936) of asphaltenes from six different bitumens show that theyare composed of from to 90 per cent carbon, 6 to 10 per cent hydrogen,0.6 to 8 per cent sulfur, and a small proportion of oxygen and ash, withpossibly nitrogen and traces of chlorine present.

The amount of asphaltenes employed according to the invention range from0.001 to 0.2 weight per cent, preferably 0.01 to 0.1 weight per cent.

In the preparation of the lubricating compositions, various mineral oilsare employed. Generally these are of petroleum origin and are complexmixtures of many hydrocarbon compounds. Preferably the mineral oils arerefined products such as are obtained by wellknown refining processessuch as by hydrogenation, polymerization, dewaxing, etc. Frequently, theoils have a Saybolt viscosity at 100F in the range of about 60 to 5,000and a Saybolt viscosity at 210F of about 30 to 250. The oils can be ofparaffinic, naphthenic, or aromatic types, as well as mixtures of one ormore types. The additives of the invention have special advantages whenemployed with paraffinic types of oil such as are obtained by solventextraction of a suitable refinery stream. Many suitable lubricatingcompositions are available as commerical products such as those used asmotor oils, fuel oils, automatic transmission oils, and the like. Theinvention is applicable to any of the lubricating oils having a problemwith respect to the viscosity when subjected to the high temperatureconditions for long periods of time.

As indicated above, the lubricating oil to be improved with respect toviscosity characteristics according to the invention preferably containsa small amount of a hydrogenated butadiene-styrene copolymer. The amountof copolymer present is generally in the range 0.5 to weight per cent,preferably 1 m3 weight per cent, of the lubricating oil.

The copolymers or VI improver additives that can be employed accordingto the invention have a molecular weight in the approximate range of25,000 to 125,000, preferably 30,000 to about 75,000. The copolymer canbe one containing from about 30 to about 45 parts by weight butadieneper 100 parts by weight of total monomers. The values for butadienecontent of the polymers are actually those of the butadiene and themonomers charged. However, these values are very close to those for thebutadiene content of the polymers because essentially completeconversion is obtained during the polymer synthesis. The copolymers havea vinyl content before hydrogenation of less than 35 weight per cent.During hydrogenation olefinic group hydrogenation is 95 weight per centor more and phenyl group hydrogenation is 5 weight per cent or less.

The copolymers can be prepared by any conventional techniques known inthe art such as those described in U.S. Pat. No. 2,975,160, R. P.Zelinski, issited Mar. 14, 1961. For example, a mixture of butadiene andstyrene monomers can be polymerized using butyllithium as a catalyst andtetrahydrofuran as a randomizing agent. The hydrogenation can be carriedout in any manner known in the art such as by the process of U.S. Pat.No. 2,864,809, R. V. Jones et al., issued Dec.'l6, 1958, or that of U.S. Pat. No. 3,113,986, D.

S. Breslow et al'., issued Dec. 10, 1963, or that of U. S.'

Pat. No. 3,025,278, S. J. Lapporte, issued Sept. 7, 1965. The copolymercan be hydrogenated over a reducednickel-kieselguhr catalyst or over anickel octoate-triethylaluminum catalyst system. The hydrogenatedbutadiene-styrene copolymers are polymers which have been sufficientlyhydrogenated to remove substantially all of the olefinic unsaturationleaving only the aromatic, i.e., phenyl group, unsaturation.

The addition of the copolymers defined above to lubricating oils toimprove viscosity index is disclosed and claimed in copendingapplication Ser. No. 686,825, filed Nov. 30, 1967, now U. S. Pat. No.3,554,911.

In addition to the copolymer, asphaltene and zinc0,0-dialkylphosphorodithioate additives of this invention, thelubricating compositions can comprise one or more of the other additivesknown to those skilled in the art such as antioxidants, pour pointdepressants, dyes, detergents, etc. Examples of these additives aremetal petroleum sulfonates, and alkyl succinimides. To be of commericalinterest as a motor oil, lubricating oil compositions ordinarily have aviscosity index of at least about 134, preferably at least about 140.

SPECIFIC EXAMPLE Tests were carried out to compare the viscosityincreases for lubricating oil samples with and without the additivecombination of the invention by heating the samples in a forced air ovenat 300F for hours.

A 20 stock oil was clay-treated with Attapulgas Clay by heating 20 partsof oil with one part of clay (by weight) to 320F. The oil was separatedby filtration through Celite. Following clay-treating, 2.5 weight percent of a hydrogenated butadiene-styrene copolymer was added to the oil.

A comparison was made between the vi's'cosities obtained with theMid-Continent SAE 20 stock thus prepared containing no additionaladditive, containing an asphaltene and zinc0,0-dialkylphosphorodithioate alone, and one sample containing both theasphaltene and zinc 0,0-dialkylphosphorodithioate. The viscosity at thebeginning and at the end of the tests were:

0.925 wt. Zinc 0,0-di (mixture of isobutyl and amyl) PhosphorodithioateThe average '01 six separate runs. A

" Added 0.72 vol. percent ofa concentrate comprising 93.6 weight percentmixed iscbutyl and amyl phosphorodithioates and 6.4 weight percent inertdiluent. The density of this concentrate was 1 .15 g./cc and the densityof the oil was 0.84 g./cc.

As can be seen from the above data, the viscosity increase at hightemperature for the lubricating oil formulation can be substantiallyreduced by the addition of both an asphaltene and a zinc0,0-dialky1phosphorodithioate in small amounts. As further demonstratedby the above data, neither additive by itself was able to minimize theviscosity increase when the lubricating oil was subjected to the hightemperature severe operation. I

The asphaltene used was Wafra asphaltene passing mesh and retained by 40mesh screen. The asphaltene was precipitated by n-pentane from a MiddleEast crude that had been topped at 1,025 "F. The asphaltene represented14.5 per cent of the charge and gave the following analysis:

Carbon 82.7 wt. Hydrogen 8.] wt. Oxygen 0.67 wt. Nitrogen 0.71 wt.Sulfur 7.7 wt.

Molecular weight was about 3,000. Metal content was:

V 0 668 parts per million MO 156 parts per million re o, 945 parts permillion I claim:

c. 0.00l-0.2 weight per cent of an asphaltene, said asphaltene beingcharacterized as a particulate material which is predominantly aromaticin character and having been separated from an asphaltic productcontaining same, and

d. 0.5-l.2 weight per cent of a zinc 0,0-dialkylphosphorodithioatewherein the alkyl groups have tw to carbon atoms.

2. A composition according to claim 1 wherein the mineral lubricatingoil is a clay pre-treated lubricating oil and said asphaltene iscomposed of from 80 to 90 per cent carbon, 6 to 10 per cent hydrogen,0.6 to 8 per cent sulfur, and a small proportion of other materialsincluding oxygen, ash, nitrogen, and chlorine.

3. A composition according to claim 1 wherein the alkyl in the zinc0,0-dialkylphosphorodithioate is a mixture of isobutyl and amyl.

4. A composition according to claim 2 wherein the mineral lubricatingoil has a viscosity at 2l0F in the range of 30-250 SUS and saidhydrogenated butadiene-styrene copolymer has a vinyl content beforehydrogenation of less than weight per cent, an olefinic grouphydrogenation of 95 weight per cent or more, and a phenyl grouphydrogenation of 5 weight per cent 1 or less.

2. A composition according to claim 1 wherein the mineral lubricatingoil is a clay pre-treated lubricating oil and said asphaltene iscomposed of from 80 to 90 per cent carbon, 6 to 10 per cent hydrogen,0.6 to 8 per cent sulfur, and a small proportion of other materialsincluding oxygen, ash, nitrogen, and chlorine.
 3. A compositionaccording to claim 1 wherein the alkyl in the zinc0,0-dialkylphosphorodithioate is a mixture of isobutyl and amyl.
 4. Acomposition according to claim 2 wherein the mineral lubricating oil hasa viscosity at 210*F in the range of 30-250 SUS and said hydrogenatedbutadiene-styrene copolymer has a vinyl content before hydrogenation ofless than 35 weight per cent, an olefinic group hydrogenation of 95weight per cent or more, and a phenyl group hydrogenation of 5 weightper cent or less.